Balanced titanium alloy

ABSTRACT

A titanium alloy containing aluminum, zirconium, silicon, at least one stabilizer from the group consisting of molybdenum, columbium, tantalum, vanadium and tungsten and which may also contain tin, all balanced in accordance with prescribed relationships.

United States Patent [72] lnventors Howard B. Bomberger, ,Ir.

Canlleld; Stanley R. Seagle, Warren, both of Ohio [21] App|.No. 713,214 [22] Filed Mar. 14, 1968 [45] Patented Nov. 9, 1971 [73] Assignee Reactive Metals, Inc.

[54] BALANCED TITANIUM ALLOY 4 Claims, 1 Drawing Fig.

[52] US. Cl.. 75/175.5 [51] Int. Cl C22c 15/00 [50] Field of Search 75/175.5; 148/32, 32.5,133

[56] References Cited UNITED STATES PATENTS 2,893,864 7/1959 Harris et a1. 75/175.5 3,049,425 8/1962 Fentiman et a1. 75/175.5

CREEP DEFDRMAT/ON, 96

Luhan Primary Examiner-Charles N. Lovell Attorney-Walter P. Wood ABSTRACT: A titanium alloy containing aluminum, zirconium, silicon, at least one stabilizer from the group consisting of molybdenum, columbium, tantalum, vanadium and tungsten and which may also contain tin, all balanced in accordance with prescribed relationships.

l l l 1 l l 1 l4 l6 I8 20 22 24 26 fiEUCT/OIV 0F AREA AFTER CREEP, X

PAIENTEDunvf 9 um 6 2 4 2P Y ohv 2, MF A -Z R 4 4 F 0 IMM H E 1 R 0 s 9 6 4 0 0 0 0 0 0 0 0 0 0 0 0 0 3 2 0 9 8 7 6 5 4 3 2 v/ .o.o.0.ooo oo INVEN TORS. HOWARD B. BOMBERGER, JR. 8.

STANLEY R. SEAGLE By Ala-(a,

A! rorney BALANCED TITANIUM ALLOY Historically, one of the main attributes of titanium and alloys of titanium has been the excellent strength-to-weight ratio of these materials for applications involving exposure to moderately high temperatures. This property has resulted in extensive use of titanium alloys in the manufacture of articles subject to exposure to temperatures of up to 850 F. However, the need for higher performance, in the aircraft industry for example, has necessitated the development of new and improved alloys capable of maintaining their desirable strengthto-weight ratio at temperatures as high as l,000 F. Material with this capability is particularly desirable in the manufacture of aircraft engine components.

The natural crystallographic grouping of titanium and its alloys involves three categories divided according to the predominant phase or phases in their microstructure. These groups are alpha, beta and mixed alpha and beta phases. In pure titanium, the alpha phase which is characterized by a hexagonal, close-packed crystallographic structure is stable from room temperature to approximately l,620 F. The beta phase of pure titanium has a body-centered cubic structure and is stable from approximately l,620 F. to the melting point of about 3,035 F.-

The hexagonal, close-packed allotrope of titanium, i.e. the alpha phase, demonstrates excellent resistance to creep. Solid solution strengthening of the alpha phase by the addition of aluminum, tin and zirconium has resulted in alloys with still better resistance to creep defonnation. However, further improvements by the addition of such alpha stabilizers is restricted due to poor thermal stability of compositions containing too great a quantity of such elements as manifested by lower ductility after creep exposure. The present invention provides a balanced titanium alloy composition which possesses improved creep strength without undue sacrifice of thermal stability or ductility after creep exposure.

In accordance with the invention there is provided a titanium alloy consisting essentially of4.0 to 7.8 percent aluminum, up to I20 percent tin, at least 0.3 percent zirconium, traces to 0.5 percent silicon and at least one stabilizer from the group consisting of molybdenum, columbium, tantalum, vanadium and tungsten, the quantity of aluminum, tin and zirconium complying with the equation:

Percent aluminum and the quantity of stabilizer being in accordance with the equation:

1.5%, and the balance essentially titanium and usual impurities.

A preferred alloy in accordance with the invention contains 4.0 to 7.0 percent aluminum, 0.3 to 7.0 percent zirconium, 2.0 to 8.0 percent tin, 0.1 to 0.35 percent silicon and 0.1 to 1.2 percent of at least one stabilizer from the group consisting of molybdenum, columbium, tantalum, vanadium and tungsten. Optimum properties have been found to be associated with a composition within the melting range 4.7 to 5.3 percent aluminum, 5.5 to 6.5 percent tin, 0.5 to 2.5 percent zirconium, 0.4 to 1.1 percent molybdenum, 0.2 to 0.3 percent silicon, more specifically having the nominal composition of 5.0 percent aluminum, 6.0 percent tin, 2.0 percent zirconium, 0.8 percent molybdenum and 0.25 percent silicon.

to a carefully formulated base composition with critically balanced alphaand beta-stabilizing elements can maximize the improvement in creep strength with acceptable thermal stability and ductility following creep exposure. It is essential, however, that the components of the alloy be critically controlled to achieve these results. Thus, for example, alloys in accordance with the invention contain 4.0 to 7.8 percent aluminum. if the upper aluminum limit is exceeded, the alloy becomes thermally unstable; similarly, a minimum of 4.0 percent aluminum is necessary to achieve acceptable mechanical properties. Zirconium has been found to enhance the creepstrengthening efi'ect of silicon and at least 0.3 percent zirconium is necessary for this purpose. Zirconium-containing alloys result in the formation of a complex compound of titanium, zirconium and silicon instead of normal titanium silicide which would form in the absence of zirconium. Some silicon is, of course, necessary for creep strengthening. However, amounts in excess of 0.5 percent are avoided to avoid ductility problems. Tin may act as a replacement for aluminum, at least in part, and is desirable, but not absolutely necessary, since it further assists in assuring thermal stability. However, over l2.0 percent tin increases the tendency toward thermal instability. A critically controlled quantity of at least one stabilizer from the group consisting of molybdenum, columbium, tantalum, vanadium and tungsten is necessary in balancing the alpha-stabilizing components to assure additional high-temperature strength while imparting thermal stability which is particularly beneficial for alloys processed or heat treated above the beta transus. However, a discovery in accordance with the invention is that the addition of the stabilizers must not exceed the alpha-solubility limit for the particular stabilizer. If the alphasolubility is exceeded, some beta phase may form that would result in a significant less of strength which may be accompanied by a loss of high-temperature stability as well.

The following examples will serve to further illustrate titanium alloys in accordance with the invention.

A series of alloys of varying compositions were prepared and samples thereof examined for tensile strength, yield strength, elongation and reduction in area, before and after creep exposure. The amount of deformation due to creep exposure was also determined. Results of these tests and the compositions involved are reported in table 1. The first sample (Alloy l is an alpha-matrix alloy which shows creep deformation of 0.23 percent. The addition of 0.8 percent molybdenum, shown in table I as Alloy No. 2, results in an improvement in creep strength as indicated by a lower percent deformation. The addition of silicon to this base, seen in Alloy No. 3, also improves the creep strength but the alloy is brittle after creep exposure. However, the combined addition of molybdenum and silicon, Alloy No. 4, results in significantly better creep strength (0.03 percent) than both of the alloys with similar individual additions, i.e. Alloy Nos. 2 and 3. Moreover, Alloy No. 4 possesses good tensile ductility after creep exposure while Alloy No. 3 is brittle.

TABLE I Before creep After creep UTS, YS, El. RA, Del'J. UTS, YS, El, RA, Alloy Composition, wt. percent K s.i. K s.i. percent percent percent K s.i. K s.i. percent percent 1 '11-6A1-8Sn-3Zr 131 114 11 26 23 127 8 12 2 Ti6Al3Sn-3Zr.8Mo. 147 10 23 14 148 123 8 15 3 Ti-6Al-3Sn-3Zr.3Si 144 128 11 24 .08 Broke in shoulder 147 128 11 22 04 146 130 13 15 4 Ti-6Al3Sn3Zr.3Si-.8Mo 1 157 141 8 18 01 155 8 14 122 18 03 156 142 12 17 24 03 139 12 20 5 Ti-GAI 3Sn 3Zr .15S1 .8Mo-.. 148 131 10 20 O4 145 132 12 20 6... Ti6Al3Sn-3Zr.3Sl-.4Mo. 144 10 21 03 156 146 10 16 7... Tl6Al3Sn3Zr.3S1-1.2Mo 156 134 11 22 09 159 141 13 16 8 Ti6A1-2Sn4Zr.2Si-2.0Mo 158 139 10 15 15 156 143 9 11 1 Creep deformation after 950 F.45 K s.i.-96 hrs.

The amounts of molybdenum and silicon added to the alloy are important in optimizing the creep strength with post creep tensile ductility. Thus, the creep strength of Alloy No. in table 1 compared with Alloy Nos. 2 and 3 indicates that the combination of beta stabilizers plus silicon, e.g. molybdenum plus silicon, even at lower silicon contents, is superior. The influence of the stabilizers, in this case molybdenum, is shown by comparing Alloy No. 3 with Alloy Nos. 4, 6 and 7 7 in table 1. The slight addition of 0.4 percent molybdenum is sufficient to impart improved creep strength. With 0.8 percent molybdenum, the excellent creep strength is still maintained. However, at the 1.2 percent molybdenum level a moderate decrease in creep strength occurs. Higher molybdenum contents, as illustrated by Alloy No. 8, further reduce the creep strength. The improvement in creep strength is believed to be limited to the solubility of the beta stabilizer, e.g. molybdenum, in the alpha phase. The maximum creep strength should occur at maximum solubility which is about 0.8 percent for molybdenum. Other beta stabilizers added in amounts within the alpha-solubility limit also improve creep strength. These limits may be exceeded to some extent, within the purview of the invention, but atsome loss of creep strength. Actual alpha-solubility limits are: tanta1umup to 7.5 percent; columbiumup to 3.0 percent; molybdenumup to 0.8 per- Additional compositions described in table 111 further illus- |5 trate the importance of adjusting the beta stabilizer content As is shown by comparing Alloy Nos. 1, 2 and 3, the beneficial influence of silicon is clearly related to the creep strength However, post creep ductility is improved by the combination of beta stabilizers and silicon.

The importance of zirconium in the alloy system in accordance with the invention is shown in the examples in table lV. With zirconium, higher creep resistance is obtained. The zirconium addition results in the formation of a complex (TiZr) Si compound which benefits creep resistance. Thus, a

minimum quantity of zirconium is necessary to improve creep cent; vanadium-up to 1.5 percent; and tungsten-up to 1.0 strength.

TABLE 11 Before creep After creep UIS, YS. El, RA, 1)ef. UIS, YS, El, RA Alloy Composition K 5.1. K 5.1. percent percent percent K s i K s.i. percent percen' 1 Ti-6A1-3s -3Zr-3Si 144 128 11 24 .08 Broke in shoulder 2 Ti6A1-3Sn-3Zr.3Si-0.8l\Io. 157 141 8 18 .01 140 8 i- 3 Ti6A1-3Sn3Zr.3Si-1.5V 153 134 7 17 02 151 136 7 1. 4.. Ti6Al-3Sn3Zr.3Si-1.0W 152 137 J 10 .03 154 146 3 5 Ti-6Al-3Sn-3Zr 1 131 114 11 26 23 127 I 120 8 1: Ti-6Al-3Sn-3Zr+0.5\l' 131 115 14 20 135 120 14 22 7, Ti-6Al-3Sn-3Zr-l-L0W 143 132 11 22 13 145 13'.) 7 1! Ti-6Al3Sn3Zr-1.5W 146 133 11 27 11 140 13) 8 1f 'Ii-6A13Sn3Zr-1.0W+0.8Mo 154 134 11 20 13 153 130 12 2 'Il6Al-3Sn3Zr-1.0\l'+0.8M0+.3S 160 135 11 15 .00 162 140 10 1 'Ii-6A1-3Sn-3Zr-0.8Mo-.3Si-1.3Cb 161 142 10 13 1 08 157 140 8 1 Creep deformation after 950 F. K s.i.96 hrs. 7 Creep deformation after 1,000 F.45 K 51-06 hrs.

TABLE III Before creep After creep Composition, wt. percent UTS, YS, E1, RA, Dell, U'IS. YS, El, RA Alloy A1 Sn Zr Mo Si K 5.1. K s.i. percent percent percent K s i K 5.1. percent percent 6 3 3 0. 8 30 156 141 10 18 03 156 142 12 11 5 1 1 0. 4 20 133 11 27 16 134 10 2'. 7 5 1 1. 2 .40 153 11 17 .04 150 132 5 ll 7 1 5 1. 2 .20 161 138 10 14 .04 162 144 3 5 5 5 O. 4 20 144 128 J 26 04 144 130 11 ll 5 5 1 1. 2 40 158 134 10 22 05 158 137 11 21 5 1 5 1. 2 .40 157 134 8 13 04 155 133 8 1. 7 5 5 0.4 40 149 144 1 2 06 Brittle 6 3 3 0. 8 15 148 131 10 20 04 145 132 12 21 4 12 0 1. 2 30 151 131 10 17 50 154 138 7 11 5 9 0 1. 2 30 159 12 17 12 153 134 12 11 5 J 2 O. 8 30 158 135 9 17 04 160 143 2 t 5 8 2 0. 8 15 04 152 138 13 11 5 8 2 0. 8 30 .02 162 146 8 15 5 J 0 0 0 131 116 18 32 1. 10 128 120 17 31 5 J 0 1. 2 0 150 128 12 11) .30 140 131 13 25 6 3 3 0 0 131 114 11 26 23 127 120 8 1i 6 3 3 0 3 144 128 11 24 08 Brittle 6 3 3 0 2 5 155 142 11 26 10 156 145 6 0 6 O 2 0 120 117 13 31 70 134 126 14 21 6 0 6 0 1 .3 144 132 10 20 13 138 130 10 1' 5 5 5 0 0 129 113 12 29 26 130 121 12 21 5 5 5 0 .3 143 127 10 21 .14 143 131 13 1! 6 3 3 1. 2 3 156 134 11 22 00 141 13 ll 6 3 3 0. 4 .3 144 10 21 .03 156 146 10 1| 1 Creep deformation after 950 F.45 K s.1.96 hrs. 2 a-l-fl anneal.

TABLE IV Before creep After creep UTS,. YS, El, RA, Dem, UTS, YS, El, RA, Alloy Composition, wt. percent K s.1. K 5.1. Percent Percent Percent K s.i. K 5.1. Percent Percent 1 Ti-5A19Sn1.2Mo-O.3Si 135 12 17 12 153 135 1'2 18 2 T1-5A19Sn-0 .8M0O.3Si2Zr. 159 135 U 17 .02 160 143 3 6 1 Creep deformation after 950 F.45 K 51-96 Hrs.

it has been further determined that optimum creep strength is achieved by beta processing or heat treatment, and in this connection, the balanced composition of the invention is a particular advance over present commercially available materials. However, optimum yield strength in titanium alloys of the type described is developed by processing, e.g. heat treating, in such a manner so as to avoid the formation of a transformed beta structure. A typical process to develop optimum yield strength involves (1) working to an end temperature below the beta transus temperature or (2) working to an end temperature below the beta transus temperature plus a heat treatment below that temperature.

As indicated previously, balancing of the elements in the alloy must be carefully controlled to achieve maximum benefits from the invention. Various possibilites exist, however, to select particular optimum compositions for specific purposes. For very severe applications requiring creep deformation of less than 0.1 percent together with high thermal stability, i.e. demonstrating a greater than percent reduction in area upon creep exposure, the compositions should be adjusted, within the limits described above, in a particular manner. It has been determined that adjustment of the aluminum, tin, zirconium, silicon and beta stabilizer contents so as to comply with certain hereinafter described creep and stability equations will result in alloys of a high order of creep resistance and thermal stability. Equations useful for this purpose are:

A. Creep Resistance: (Permanent deformation after creep exposure X100) l0z362.6(%A1)-1.1(%Sn)0.7(%Zr)-27(%Sl)--3(Mo,); B. Stability: (Reduction in area after creep exposure) 10570-72(%Al).25(%Sn)-l.5(%Zr)27.5(%Si)'-0(% M0,).

The symbol M0, in the above equations refers to molybdenum content or molybdenum equivalency of other stabilizers, i.e. columbium, tantalum, vanadium and tungsten. Molybdenum equivalency is expressed by the equation:

Creep and stability according to the equations A and B above are determined by testing specimens at 950 F, under with respect to aluminum and tin on creep strength and thermal stability. The graph is related to a base composition of Ti- XAl-YSn-2Zr-0.8Mo-0.25Si based upon an instability threshold of less than 8 where the aluminum, tin and zirconium, ie the alpha stabilizers, are related by the equation:

ln the graph, the sloping line represents the tin content for different aluminum levels at which the loss of ductility is disproportionately greater with increase in creep strength, that is, the point at which the equations discussed above are no longer applicable.

it is apparent from the above that various changes and modifications may be made without departing from the invention. Accordingly, the scope of the invention should be limited only by the appended claims wherein what is claimed is:

1. A titanium-base alloy consisting essentially of about 4.7 to 5.3 percent aluminum, 5.5 to 6.5 percent tin, 0.5 to 2.5 percent zirconium, 0.4 to 1.1 percent molybdenum, 0.2 to 0.3 percent silicon, and the balance titanium and incidental impurities, said alloy being characterized by improved creep strength without undue sacrifice of thermal stability or ductility after creep exposure.

2. A titanium alloy In accordance with claim 1 containing 5.0 percent aluminum, 6.0 percent tin, 2.0 percent zirconium, 0.8 percent molybdenum and 0.25 percent silicon.

3. A titanium alloy in accordance with claim 1 additionally containing 0.53 to 1.33 percent vanadium.

4. A titanium alloy in accordance with claim I additionally containing 0.8 to 2.0 percent tungsten t a a t UNITED STATES PATENT OFFIGE CERTIFICATE OF CORRECTION Patent No. 3,619,184 Dated November 9, 1971 Inventor(s) Howard B. Bomberqer, Jr, et a1 It is certified that error appears in the above-identified patent and that: said Letters Patent are hereby corrected as shown below:

Column 1, line 51, before "0.75" delete "c". Column 2, line 43, "less" should 'read loss Column 3, line 8, delete the second "7". Column 4, Table II, the last column should read l4 l5 12 22 l2 12 21 ll and the last column of Table III should read 17 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,619,184 Dated November 9, 1971 Inventor(s) Howard B. Bomberger, Jr., et a1 2 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

l6 Column 5, line 30, "51" should read Si and before "Mo insert line 38, before "0.75" delete "c".

Signed and sealed this 14th day of November 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents M F'O-IOSO KID-691 USCOMM-DC 60376-P69 u 5 GOVERNMENT PRmTm orncs I989 0- 366-334, 

2. A titanium alloy in accordance with claim 1 containing 5.0 percent aluminum, 6.0 percent tin, 2.0 percent zirconium, 0.8 percent molybdenum and 0.25 percent silicon.
 3. A titanium alloy in accordance with claim 1 additionally containing 0.53 to 1.33 percent vanadium.
 4. A titanium alloy in accordance with claim 1 additionally containing 0.8 to 2.0 percent tungsten. 